1. Field of the Invention
The invention provides an organic thin film transistor array substrate, and in particular, an organic thin film transistor array substrate having an alignment film, formed in the same process step using the same material, in the OTFT area and the LCD area.
2. Description of the Related Art
Organic semiconductor material has been lauded by many international research institutes, as one of the most promising materials for producing thin film transistors and other electronic and optic-electron elements. Sirringhaus etc. of the University of Cambridge, discloses the process of producing OTFT by self-organization of organic molecules to obtain alignment of various anisotropic structures. Better alignment of the molecular chain results in enhanced electric charge transportation efficiency. Carrier mobility of the transistor increases at least 100 times, thereby proving that the alignment of organic molecules does have importance in enhancing electric properties (Nature, Vol. 401, p. 685, 1999).
Organic thin film transistors use an organic layer as the active layer, and have been applied in driving liquid crystal displays (LCDs). In order to simplify process and reduce production costs, an integration of LCD and OTFT on the same substrate (monolithically) has been proposed.
Kabushiki Kaisha Toshiba discloses in U.S. Pat. No. 5,355,235, the incorporation of a bottom-gate OTFT structure having two organic layers for a permissive LCD.
Mitshubishi Denki Kabushiki Kaisha discloses in U.S. Pat. No. 6,060,333 the incorporation of bottom gate OTFT structure for a permissive or reflective LCD. In this method, OTFT exhibits unsatisfactory electric properties and there is no LC alignment film.
Hitachi Ltd. Discloses in U.S. Pat. No. 6,300,988 B1 the incorporation of a bottom gate OTFT structure with an LCD. A patterned insulation layer is used to pattern the deposited organic semiconductor, such that the channel region and the non-channel region are isolated. As a result, leakage and crosstalk among elements are reduced. However, the organic semiconductor in the OTFT not control the alignment, thus the electrical properties are unsatisfactory and the process is more complicated.
In the above-mentioned OTFT and LCD integrated elements, the organic semiconductor of the OTFT is not aligned; therefore electrical properties are not satisfactory and do not meet circuit design requirements. Additionally, if compatible OTFT and LCD processes are not utilized properly, process complexity increases.